The storage of energy, for example heat-generating energy, makes it possible to stagger the production and the consumption of that energy in time.
The storage of heat-generating energy is also useful for upgrading soft energies, such as solar energy, which are renewable but whose production is intermittent. The storage of the energy can also be useful to exploit the electricity price differences between the so-called “off-peak” hours during which the electricity tariffs are lowest, and the so-called “peak” hours during which the tariffs are highest. For example, in the case of energy storage by air compression, generating heat-generating energy which is stored in a heat regenerator, the compression phases consuming electricity are advantageously performed at lower cost during the off-peak hours, whereas the expansion phases producing electricity are performed during the peak hours, in order to provide electricity which can be injected into the electricity network, according to demand, at an advantageous tariff.
The heat-generating energy is conventionally stored in a packed bed of energy storage elements, or “media”, of a regenerator, for example in a packed bed of pebbles.
The storage operation, based on heat exchange between a current of heat-generating fluid and the regenerator, is conventionally called the “charge”, the heat-generating fluid entering into the generator at the time of the charge being called “charge heat-generating fluid”.
The transfer of heat-generating energy can result in an increase in the temperature of these energy storage elements (storage of “sensible” heat) and/or to a change of state of these elements (storage of “latent” heat).
The stored heat-generating energy can then be recovered, by heat exchange between a current of heat-transfer fluid and the energy storage elements. This operation is conventionally called “discharge”, the heat-generating fluid entering into the regenerator at the time of the discharge being called “discharge heat-generating fluid”.
“A review on packed bed solar energy storage systems”, Renewable and Sustainable Energy Reviews, 14 (2010), p 1059-1069 describes the state of the art in the field of regenerators.
U.S. Pat. No. 4,651,810 describes a glass furnace regenerator comprising energy storage elements obtained from chromium ore. DE 36 17 904 provides a composition for a chromium ore: between 1% and 6% of SiO2, between 0.3% and 0.4% of CaO, between 13.6% and 29.6% of Fe2O3 and between 8.7% and 28.9% of Al2O3.
WO 2004/063652 describes an insulating brick for an industrial furnace made of a material comprising 50% iron oxide.
None of these documents describes a regenerator comprising a packed bed of energy storage elements made of a material having the characteristic: Fe2O3+Al2O3+CaO+TiO2+SiO2+Na2O>80%.
When a regenerator is operating, and in particular when the heat-transfer fluid is moist air, the condensates from the moisture of the air corrode the materials of the regenerator. What is more, at high pressures, the water present in the air may condense and mix with the other condensates or pollutants that are present. The latter can thus render the water acid and therefore corrosive. The result of this is a considerable reduction in the life of the regenerator, which should be greater than 20 years, even greater than 30 years in industrial installations, and therefore an increase in the overall cost.
There is therefore a need to increase the life of the regenerators, particularly with regard to corrosive acid attacks, in particular at operating temperatures greater than 350° C., even greater than 500° C., and in particular for regenerators charged with moist air.
One aim of the invention is to at least partially satisfy this requirement.